#include<stdio.h>
#include<math.h>
void main()
{
	int sign=1;
	double pi=0,n=1,term=1;
	while(fabs(term)>=1e-6)
	{
		pi=pi+term;
		n=n+2;
		sign=-sign;
		term=sign/n;
	}
	pi=pi*4;
	printf("pi=%10.8f\n",pi);
}
